set GUILE env var when building gnutls, fixes issue #11601 (#11607)

var/spack/repos/builtin/packages/gnutls/package.py

@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 from spack import *
+import os
 
 
 class Gnutls(AutotoolsPackage):
@@ -45,6 +46,12 @@ def url_for_version(self, version):
         url = "https://www.gnupg.org/ftp/gcrypt/gnutls/v{0}/gnutls-{1}.tar.xz"
         return url.format(version.up_to(2), version)
 
+    def setup_environment(self, build_env, run_env):
+        spec = self.spec
+        if '+guile' in spec:
+            build_env.set('GUILE', os.path.join(spec["guile"].prefix.bin,
+                                                'guile'))
+
     def configure_args(self):
         spec = self.spec
         args = [